Optical scanners operate by detecting light from a medium, such as a sheet of paper, using a photosensor and deriving a digital image from the detected light. The light may be provided by an illumination source within the scanner. To allow the scanner to properly translate the detected light into a digital image, scanners typically calibrate the photosensor using a background with a relatively light color. A relatively light color background may provide the maximum amount of light to the photosensor in the calibration process.
In the process of scanning from medium, however, a relatively light color background may make it difficult for the scanner to detect the edges of a medium being scanned. In addition, a relatively light color background may also cause light to be reflected off of the background and through the medium to result in undesirable “bleed through” of the medium. To avoid these problems, scanners may use a relatively dark background during the process of scanning from medium.
The use of different backgrounds in the calibration and scan operations of scanner may result in added complexity in the scanner and higher costs.